1. Field of the Invention
The present invention relates to devices for releasably binding together a stack of perforated paper, and in one aspect to such devices which are easily releasable to add or delete sheets.
2. Description of the Prior Art
The prior art is replete with devices for releasably binding together a stack of perforated paper. U.S. Pat. Nos. 1,790,693, 2,057,514, 2,120,659, 2,193,181, 2,315,303, 2,318,941 and 3,734,634 and French Pat. No. 800,994 are specifically noted.
Of the devices described in these patents, the device described in U.S. Pat. No. 2,057,514 is believed to be the closest prior art. Like the present invention, the device described in that invention includes a pair of rake-like members, each comprising a row of studs projecting from a rail and having openings in the rail shaped to receive end portions of the studs from the other rail. The studs and openings are spaced so that the rake-like members can be assembled to form a ladder-like assembly with the studs passing through the perforations in the paper and the strips on opposite sides of the stack. The device also includes a backing strip shaped to define channels with opposed open sides which channels will slidably receive the rails of the ladder-like assembly with the backing strip extending around the spine edge of the stack of sheets. The ladder assembly is releasably retained in the backing strip by end portions of the rails adapted to engage the ends of the channels defined by the backing member and to center the ladder assembly therein.
The device described in U.S. Pat. No. 2,057,514, however, is a metal structure which is more expensive than may be desired for many applications. Only projections from the rails are positioned in the opposed channels when the ladder-like assembly is slid into engagement therewith so that the channels project a greater distance beyond the rails away from the adjacent surface of the paper than is desirable to provide a compact binding device. The ends of the studs make snap engagement with the openings in the rails which restricts easy assembly and disassembly of the ladder assembly. Also the end portions of the rails are not easily disengaged from the ends of the channel member since the end portions of the rails must first be squeezed together so that they are disengaged from the ends of the channels and the ladder assembly must then be slid by a separate movement to move the end portions into the channel and afford movement of the ladder-like assembly therefrom.